Valetini returns to blindside flanker after recovering from injury and is one of three changes to the starting forward pack, along with Will Skelton and hooker David Porecki who are set to face the Lions for the first time in a Test match.
Porecki will link up with James Slipper and Allan Alaalatoa in an experienced front row, while Skelton will partner with Nick Frost as the run-on locks.
The backline remains unchanged from the one that started at Suncorp Stadium, with Jake Gordon and Tom Lynagh again the halves pairing.
Wallaby number 944 Len Ikitau and 21-year-old Joseph-Aukuso Suaalii will continue to build on their midfield combination, while Melbourne product Harry Potter will play his first Test in his hometown on the left wing. Max Jorgensen lines up on the right edge and flyer Tom Wright will again start at fullback.
The coaches have continued with the same front-row replacements of Billy Pollard, Angus Bell and Tom Robertson, in what will be the Wallabies' 700th Test match.
Jeremy Williams will take on a finishing role as the replacement lock, with Langi Gleeson returning from injury and the energetic Carlo Tizzano the remaining forward cover.
Livewire Tate McDermott has been confirmed as the substitute scrumhalf, while Ben Donaldson will get a chance to showcase his versatility, named in the number 23 jersey.
"The squad has recovered well after a very physical first test and the week's preparation here in Melbourne has allowed us a bit more time together," said Wallabies coach Joe Schmidt.
"We took some confidence from the second half last week, but we know we'll need to improve further against a Lions team that will bring plenty of fire to the contest on Saturday night."
Australia - 15 Tom Wright, 14 Max Jorgensen, 13 Joseph-Aukuso Suaalii, 12 Len Ikitau, 11 Harry Potter, 10 Tom Lynagh, 9 Jake Gordon, 8 Harry Wilson (c), 7 Fraser McReight, 6 Rob Valetini, 5 Will Skelton, 4 Nick Frost, 3 Allan Alaalatoa, 2 David Porecki, 1 James Slipper.
Replacements: 16 Billy Pollard, 17 Angus Bell, 18 Tom Robertson, 19 Jeremy Williams, 20 Langi Gleeson, 21 Carlo Tizzano, 22 Tate McDermott, 23 Ben Donaldson.
Andy Farrell has described the dramatic moment during Thursday's training session in Melbourne when Garry Ringrose approached him to say he could no longer take his place in the Lions side for Saturday's Test.
Andy Farrell has named his son Owen on the bench for the second British and Irish Lions Test against Australia at the MCG in Melbourne on Saturday night.
Wallabies back Harry Potter has strongly dismissed former England and British & Irish Lions coach Sir Clive Woodward's accusation that Australian rugby is plagued by a "losing mentality."
The British and Irish Lions narrowly avoided a slip-up in their final midweek tour match, scraping past a spirited First Nations & Pasifika XV 24-19 in Melbourne on Tuesday.
